1. Field of the Invention
The present invention relates to a television signal processing apparatus which is capable of transmitting video signals having a different aspect ratio from that of the existing television systems, while being compatible with the existing television system.
2. Description of the Prior Art
In Japan, over 20 years have passed since the color television broadcast under the existing NTSC (National Television System Committee) system started in 1960. During that period of time, various new television systems have been proposed in response to the needs of a high definition picture and due to the improvements of performance of television receivers. The contents of TV programs broadcasted have been changed from mere studio-made programs or relay programs to programs providing images of high pictorial quality which make impressions of a presence of an actual scene, such as the cinema-sized broadcasting of movies.
The specifications of the existing television broadcasting are as follows: the number of scanning lines: 525, interlace scanning, luminance signal horizontal bandwidth: 4.2 MHz, aspect ratio: 4 : 3. (cf., i.e. a publication on the broadcast technology, titled "Color Television" edited and issued by The Japan Broadcasting Corporation (NHK) 1961) When a movie is put on the air, the picture size of the movie must be adapted to the aspect ratio of 4 : 3 of the existing television receivers by cutting both sides of the movie picture or by providing dead spaces on the upper and lower regions of a tube face so that the aspect ratio of the usual picture area will corresponding to the value of the movie.
As described above, there lies a problem that when a movie or a picture from which one may receive impressions of an actual presence in a scene is televised under the existing broadcast system, a part of the picture is to be cut or the area of the picture must be reduced, thereby failing to convey a complete message of the producer. A mere transmission of signals having a larger aspect ratio than that of 4 : 3 would disable the ordinary TV sets from receiving said signals in a normal manner. With the number of scanning lines and the frame frequency being equal to those of the existing broadcast system, in order to obtain the same horizontal resolution, the video bandwidth which is m/4 times bigger than that of the existing aspect ratio is required with respect to the aspect ratio of m : 3 (m is an actual number larger than 4). However, in view of the effective utilization of electric wave resources, it is impossible to widen a transmission band in a disorderly manner.
A number of methods are here considered for widening the aspect ratio while remaining compatible with the existing television system. For example, when an original picture is picked up with an aspect ratio of m : 3 which has a larger frame size than the conventional one, firstly the video signals are time-axis expanded by m/4 times which correspond to the portion appearing on the tube face of the existing television receiver with the aspect ratio of 4 : 3. In order to obtain information of picture area with an aspect ratio of m : 3, among the remaining portions of the video signals, the low frequency component will be transmitted by way of time-axis multiplexing and the high frequency component by non-time-axis multiplexing, that is, multiplexing methods such as quadrature modulation or frequency interleaving or other methods which are not time-division multiplexing methods, (see our U.S Pat. application No. 070804 filed Jul. 7, 1987 and U.S Pat. application No. 174452 filed Mar. 23, 1988 and "A Single Channel NTSC Compatible Widescreen EDTV System" by M. Isnardi et al, HDTV Colloquium in Ottawa, Oct., 1987). FIGS. 12(a)-12(c) are a spectrum views showing a non-time-axis multiplex processing method of one embodiment of the prior art. FIG. 12(a) is a spectrum view of a television signal amplitude-modulated for vestigial side band. FIG. 12(b) shows a multiple signal other than the television signal as shown in FIG. 12(a) wherein the multiple signal is a modulated version for a vestigial side band of a carrier P2 which is same in frequency as carrier P1 but out of phase therewith FIG. 12(c) shows a multiplexing of the signal of FIG. 12(b) and the signal of FIG. 12(a). The bandwidth of the multiple signal is not restricted to this.
As for the method for non-time-axis multiplex processing, there is a method wherein multiplexing takes place in the first and third quadrants which are positions conjugate to chrominance sub carriers on the temporal-vertical two-dimensional frequency plot (see Japanese Laid-Open Patent Publication No. 59-171387).
However, there was no clear and concrete indication of how the luminance and chrominance signals of the video signals as well as the time-axis will be processed in such methods.